Discharge device and method of making



April 14, 1942. J, LEMPERT ETAL 2,279,831

DISCHARGE DEVICE AND METHOD OF MAKING Filed April 30, 1941 .3l ZZ JZ INVENTORS J.- EM/75er J5 M ff, STEM/wer. 39 B f Agmm ATTO R N EY Patented Apr. 14, 19.42

DISCHARGE DEVICE AND METHOD OF MAKING Joseph Lempert, Montclair,

and Nelson ll.

Stewart, Caldwell, N. J.. assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 30, 1941, Serial No. 391,124

(Cl. Z50-27.5)

15 Claims.

This invention relates to discharge devices and methods of making, and more particularly to electrodes and methods of connecting the supporting elements thereto.

The principal object of our invention, generally considered, is the production of discharge devices involving composite parts, such as are formed when a copper anode is connected to a supporting stem formed of nickel-cobalt-iron alloy, generally designated as Kovar."

Another object of our invention is the uniting of dissimilar electrically-conducting materials which cannot be welded or soldered together in a conventional way.

A further object of our invention is to unite dissimilar metals by another metal of lower melting point, while at the same time preventing intergranular penetration of one oi said metals by avoiding tensile strains.

A still further object of our invention is the production of a copper electrode or portion thereof united to a sleeve of Kovar.

Other objects and advantages of the inventionI relating t the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

Referring to the drawing illustrating our invention:

1 is an elevational view, partly in axial section, showing an X-ray tube embodying our invention.

Fig. 2`is a fragmentary axial sectional view of a portion `of the apparatus shown in Fig. 1, before the anode and supporting element have been connected.

Fig. 3 is a view corresponding to Fig. 2, but showing the parts after the brazing operation has. been completed\ and the parts securely connected.

Fig. 4 is a fragmentary elevational view, partly in axial section, showing the grid structure of a radio transmitting tube, the copper base portion thereof, and Kovar supporting means securing the latter to the glass of the enclosing envelope.

Referring to the drawing in detail, like parts being designated by like reference characters, and first considering the embodiment of our invention illustrated in Figs. 1, 2 and 3, there is shown an X-ray tube II, comprising a vitreous or glass envelope I2, enclosing a cathode assembly Il, includingan incandescible cathode (not seen) in Fig. 1, and an anode or target assembly I4. The leads for the nlamentary cathode are connected toy terminals I5 and I8, and the anode Il has a heavy lead I'I which may be threadably connected thereto, as indicated at I8, and have attached thereto cooling means such as heatradiating iins I9.

The target proper 2| consists of a copper base portion 22, and a target insert of refractory material such as tungsten 23. The means for supporting the copper element 22 from the envelope I2, consists in this instance of a sleeve or hollow cylindrical member 24 of an alloy designated as Kovar, which alloy consists of from 28.7 to 29.2% of nickel, 17.3 to 17.8% of cobalt, 52.9 to 53.4% of iron, not more than .06% of carbon, not more than .5% of manganese, and not more than .2% of silicon.

The reason for using a sleeve of this construction is that it has a coeillcient of expansion approximating that of hard or borosilicate glass customarily used for making X-ray tube envelopes. If connected to soft glass, a sleeve of corresponding alloy, such as nickel-iron, 'may be substituted.

The conventional method of constructing a Kovar seal for an electronic tube having a copper electrode of sizable cross-section, is to machine the copper to an appropriate dimension, wrap solder or a brazing alloy around the copper, and place the Kovar seal sleeve over the solder. This assembly was th'en heated in a protective atmosphere, such as hydrogen, until the solder or brazing alloy melted and secured the parts together.

Since it is desirable to maintain the layer of connecting material at a minimum, it would be better to make the Kovar a tight fit on the copper, but such construction would introduce tensile strains in said Kovar during brazing, with the possibility of causing intergranular penetration to such an extent that cracking would ensue.

'I'he construction covered by the present application, was originated when investigation of a number of leaky X-ray tubes disclosed that the leaks were through cracks in the Kovar, which resulted from intergranular penetration of the employed silver solder occurring during the brazing operation.

Our construction at that time, consisted of a solid copper anode with ribbon solder wrapped around a shoulder, over which a Kovar" sleeve was placed prior to the soldering or brazing operation. Since this was a rather tight t, and

the coefficient of expansion of copper is several times that of Kovar," the latter was under an appreciable tensile strain when the junction was heated to the brazing temperature of about 900 C. r

We attempted to relieve this condition by loosening the t, but in spite of this, we continued to encounter dilculty since the t became more or less a matter of operator judgment. We then changed the construction to that shown in Figs. l, 2 and 3, boring out the copper anode portion 22 to provide the cavity or pocket 25, or portion surrounded by the peripheral flange 25, inserting the Kovar sleeve or hollow rod 24, and placing a ring of wire solder or brazing alloy 21, of lower melting point than either copper or Kovar, in the position illustrated, So that it would ilow into the joint at brazing temperature, when heated in a hydrogen furnace, for example, and be carried upward after melting by capillary attraction to provide the brazed connection designated as 28 in Fig, 3.

Since the Kovar coefllcient of expansion is but a fraction of that of copper, the copper expanded away from the "Kovar at brazing temperatures, leaving the Kovar free of any applied stress at that time, thus reducing the speed of intergranular penetration with subsequent cracking and leaks.

The other advantages found are that solder or brazing material in Wire form is cheaper than in ribbon form, it is no longer necessary to depend upon the operators judgment as to nt, a thinner section of brazing material may be maintained,`

the finished piece presents a better appearance, the eiiiciency of cooling the brazed joint on exhaust is improved, and a lower shrinkage from leakers due to cracked Kovar is experienced.

Initially we applied a ring of solder or brazing material in the position indicated in dotted lines and designated as 21 in Fig. 2. However, this has been superseded by the better arrangement, previously described, in which the brazing material rises by capillary attraction, rather than running into the junction by gravity, and forms an even lillet at the exposed part of the joint, designated by the reference character 28 in Fig. 3.

' As a suitable brazing alloy in the present instance, we prefer one of silver and copper which has a melting point lower than that of copper, such as 50-50 alloy or the eutectic alloy, comprising approximately 70% silver and 30% copper. Other alloys having suitable melting points may be employed, provided their vapor pressures are low.d

The other end of the Kovar sleeve 24 is united to the re-entrant portion 29 of the glass envelope l2 by having its outer edge portion embedded therein by a fused glass seal, as indicated at 3|. On account of the similarity in the coefficients of expansion, a very good seal is produced, and such a tube will stay vacuum-tight as desired.

Referring now to the embodiment of our invention illustrated in Fig. 4, there is shown a portion of a radio transmitting tube, having a vitreous or glass envelope 32, only the reentrant portion 33 serving to support the electrode assembly 34, being illustrated.

The electrode assembly 34 comprises a grid structure mounted on a base 35 of copper, in

turn supported by Kovar sleeve 36, the lower or outer edge portion of which is secured to the re-entrant glass portion 33, by being embedded therein to form a fused glass seal as indicated at 37.

The copper base portion 35 has a cavity 38 therein, corresponding with the cavity 25 of the preceding embodiment, in which cavity is iltted the upper or inner end of the Kovar sleeve 36, and secured thereto by brazing in a manner such as previously described in connection with the preceding embodiment.

As in said preceding embodiment, the electric connection with the electrode 34, is made by means of a lead member 39, the inner end of which is threadably connected to the copper base 35, as indicated at 4i. The Kovar to glass seal may be protected from corona and consequent puncture by means of a skirt 42, the upper or inner portion 43 of which is threadably connected to the exterior of the copper member 35.

Although we have disclosed a preferred embodiment of our discharge device, involving'a seal made by brazing Kovar" in a cavity in copper, it will be understood that we do not wish to be limited to the exact combination, as the supporting member 24 or 36 need not be hollow. some other material, such as silver, may be substituted for copper, and another alloy or metal adapted to seal directly to the glass of the envelope used, such as nickel-iron alloy, may be substituted for the Kovar or nickel-cobalt-iron alloy preferred, within the broad scope of our invention.

Although preferred embodiments of our invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

l. A discharge device comprising a vitreous envelope, an electrode sealed therein, said electrode comprising a metal element having a cavity, a hollow rod of o material adapted to seal directly to the material of the envelope disposed in said cavity, and brazing material fused in and filling the space in said cavity around the received open end portion of said rod, said rod having its other end portion sealed directly to the material of said envelope.

2. A discharge device comprising a vitreous envelope, an electrode sealed in said envelope, said electrode comprising a copper element having a cavity, a sleeve oi material adapted to seal directly to the material of the envelope, and a brazing alloy fused in and illing the space in said cavity around the received open end portion of said sleeve.

3. A discharge device comprising a vitreous envelope, an anode sealed therein, said anode comprising an element of a metal such as copper, having a cavity, a rod oi' a material auch as nickel-cobalt-iron alloy adapted to seal directly to the material of the envelope disposed in said cavity, and brazing material fused in and illllng the space in said cavity around the received end portion of said rod, said rod having its other end portion sealed directly to the material of said envelope.

4. A discharge device comprising a vitreous envelope, an incandescible cathode and associated anode sealed in said envelope, said anode comprising a copper element having a cavity, a sleeve of nickel-cobalt-iron alloy of a composition adapted to seal directly to the material of the envelope, and a brazing alloy fused in and lilling the space in said cavity around the received end portion of said sleeve, said envelope having a re-entrant portion and the outer portion oi' said sleeve being embedded therein.

5. A discharge device comprising a vitreous envelope having a copper anode member disposed therein, a lead for said member secured thereto, and a sleeve of nickel-cobalt-iron alloy surrounding said lead and tting a cavity in said member, and brazingvalloy fused and filling the space in said cavity around the received end portion of saidsleeve.

6; A composite assembly comprising a sleeve of an alloy adapted to seal directly to glass, an element of metal, a cavity in said element receiving an open end portion of the sleeve, and a fused brazing alloy of lower melting point than either of said elements filling the space in said cavity around the received portion of said sleeve.

7. A composite assembly comprising an element of nickel-cobalt-iron alloy, an element of copper, a cavity in one of said elements receiving an end portion of the other, and a fused brazing alloy of lower melting point than either of said elements filling the space in said cavity around the yreceived end of said otherelement.

8. A composite assembly comprising an element of Kovar, an element of copper, a cavity in one of said elements receiving an end portion of the other, and a fused brazing alloy, of lower melting point than either copper or Kovar, till:- ing the space in said cavity around the received end of said other element.

9. A composite assembly comprising an element of Kovar, an element of copper, a cavity in the copper element receivingY an end portion of the Kovar element, and a fused brazing alloy, oi' lower melting point than either copper or Kovar, filling the space in said cavity around the received end of sai-d Kovar" element.

10. A compositeassembly comprising an elef ment formed of nickel-cobalt-iron alloy, an element oi copper, said copper 'element having a cavity receiving the `end portion of the other, and a silver copper brazing alloy filling the space in said cavity around the received end portion of said other element.

11. A composite assembly comprising an element formed of nickel-cobalt-iron alloy in which the nickel ranges between 28.7 and 29.2%. the

cobalt between 17.3 and 17.8%, and the iron between 52.9 and 53.4%, an element of copper, said copper element having a cavity receiving an end portion of the other, and a brazing alloy consisting of between and 70% silver, and 50 and 30% copper, illling the space in said cavity around the received end portion of said other element.

12. The method of uniting an element of metal to a hollow support element of material adapted to seal directly to glass, comprising inserting an open end of said support element into a cavity in the other lelement and lling the space in said cavity around the support element with a molten brazing alloy oi lower melting point than either of said elements.

13. The method of uniting an element of metal to a hollow support element of metal adapted to seal directly to glass, comprising inserting an open end of said support element into a cavity in the other element and iilling the space in said cavity around the support element with a molten brazing alloy of lower melting pointthan either of said elements.

14. The method of uniting an element of copper t-o a Kovar support, comprising inserting said support into a cavity in the copper and i111- ing the space in said cavity around said support with a molten brazing alloy of lower melting point than eithercopper or Kovar.

15. The method of uniting an element of copper to a support formed of a nickel-cobalt-iron alloy in which the proportion of nickel ranges between 28.7 and 29.2%, that of cobalt between 17.3 and 17.8%, and that of iron between 52.9 and 53.4%, comprising inserting an end portion of said support into a cavity in the copper and lling the space in said cavity around said end portion with a molten alloy of silver and copper in which the proportion of silver is between 50 and JOSEPH LEMPERT.

NELSON H. STEWART. 

